use correct variable in BacktraceCleaner test
use correct variable in BacktraceCleaner test

`@target_dir` variable was changed to local variable in 8e1714b.

repinel/rails,notapatch/rails,mtsmfm/rails,gcourtemanche/rails,mtsmfm/railstest,gcourtemanche/rails,rails/rails,joonyou/rails,sealocal/rails,lucasmazza/rails,hanystudy/rails,yhirano55/rails,ledestin/rails,georgeclaghorn/rails,pschambacher/rails,rossta/rails,illacceptanything/illacceptanything,rossta/rails,koic/rails,georgeclaghorn/rails,kddeisz/rails,alecspopa/rails,Vasfed/rails,illacceptanything/illacceptanything,bolek/rails,Vasfed/rails,BlakeWilliams/rails,georgeclaghorn/rails,kaspth/rails,tijwelch/rails,hanystudy/rails,illacceptanything/illacceptanything,untidy-hair/rails,fabianoleittes/rails,baerjam/rails,matrinox/rails,illacceptanything/illacceptanything,flanger001/rails,sealocal/rails,assain/rails,illacceptanything/illacceptanything,elfassy/rails,stefanmb/rails,Envek/rails,travisofthenorth/rails,MSP-Greg/rails,kmcphillips/rails,travisofthenorth/rails,starknx/rails,marklocklear/rails,lucasmazza/rails,tgxworld/rails,printercu/rails,kmcphillips/rails,prathamesh-sonpatki/rails,utilum/rails,mechanicles/rails,gauravtiwari/rails,lcreid/rails,illacceptanything/illacceptanything,bradleypriest/rails,flanger001/rails,untidy-hair/rails,mtsmfm/railstest,xlymian/rails,lucasmazza/rails,mechanicles/rails,maicher/rails,bolek/rails,yahonda/rails,yasslab/railsguides.jp,mijoharas/rails,jeremy/rails,eileencodes/rails,palkan/rails,ledestin/rails,printercu/rails,jeremy/rails,notapatch/rails,yalab/rails,repinel/rails,assain/rails,betesh/rails,iainbeeston/rails,Vasfed/rails,gfvcastro/rails,gauravtiwari/rails,kenta-s/rails,arunagw/rails,schuetzm/rails,rafaelfranca/omg-rails,tijwelch/rails,rbhitchcock/rails,kddeisz/rails,ngpestelos/rails,prathamesh-sonpatki/rails,richseviora/rails,deraru/rails,lcreid/rails,kamipo/rails,betesh/rails,yahonda/rails,voray/rails,marklocklear/rails,baerjam/rails,tgxworld/rails,yasslab/railsguides.jp,felipecvo/rails,aditya-kapoor/rails,illacceptanything/illacceptanything,baerjam/rails,lcreid/rails,kmayer/rails,kddeisz/rails,tjschuck/rails,Envek/rails,mohitnatoo/rails,Edouard-chin/rails,notapatch/rails,samphilipd/rails,alecspopa/rails,yawboakye/rails,pvalena/rails,riseshia/railsguides.kr,mechanicles/rails,matrinox/rails,gcourtemanche/rails,Edouard-chin/rails,deraru/rails,gavingmiller/rails,stefanmb/rails,mohitnatoo/rails,joonyou/rails,utilum/rails,Edouard-chin/rails,shioyama/rails,kirs/rails-1,koic/rails,EmmaB/rails-1,yahonda/rails,elfassy/rails,repinel/rails,yasslab/railsguides.jp,arunagw/rails,odedniv/rails,samphilipd/rails,ttanimichi/rails,flanger001/rails,BlakeWilliams/rails,deraru/rails,gauravtiwari/rails,EmmaB/rails-1,vipulnsward/rails,fabianoleittes/rails,voray/rails,illacceptanything/illacceptanything,Spin42/rails,ttanimichi/rails,illacceptanything/illacceptanything,brchristian/rails,tijwelch/rails,notapatch/rails,xlymian/rails,georgeclaghorn/rails,rails/rails,ledestin/rails,mechanicles/rails,mathieujobin/reduced-rails-for-travis,kenta-s/rails,vipulnsward/rails,iainbeeston/rails,jeremy/rails,illacceptanything/illacceptanything,kmayer/rails,shioyama/rails,bogdanvlviv/rails,EmmaB/rails-1,richseviora/rails,betesh/rails,BlakeWilliams/rails,pvalena/rails,schuetzm/rails,printercu/rails,gfvcastro/rails,untidy-hair/rails,richseviora/rails,schuetzm/rails,baerjam/rails,fabianoleittes/rails,MSP-Greg/rails,gfvcastro/rails,starknx/rails,bogdanvlviv/rails,kmcphillips/rails,felipecvo/rails,marklocklear/rails,Stellenticket/rails,kirs/rails-1,tgxworld/rails,matrinox/rails,rails/rails,eileencodes/rails,iainbeeston/rails,voray/rails,yhirano55/rails,lcreid/rails,iainbeeston/rails,Vasfed/rails,utilum/rails,riseshia/railsguides.kr,mathieujobin/reduced-rails-for-travis,shioyama/rails,gfvcastro/rails,arunagw/rails,brchristian/rails,Erol/rails,alecspopa/rails,riseshia/railsguides.kr,prathamesh-sonpatki/rails,repinel/rails,Stellenticket/rails,odedniv/rails,ngpestelos/rails,yhirano55/rails,bradleypriest/rails,yalab/rails,coreyward/rails,riseshia/railsguides.kr,maicher/rails,bogdanvlviv/rails,mohitnatoo/rails,Stellenticket/rails,Sen-Zhang/rails,kamipo/rails,fabianoleittes/rails,yalab/rails,illacceptanything/illacceptanything,joonyou/rails,mijoharas/rails,schuetzm/rails,illacceptanything/illacceptanything,pschambacher/rails,bradleypriest/rails,aditya-kapoor/rails,Erol/rails,palkan/rails,mtsmfm/railstest,xlymian/rails,untidy-hair/rails,travisofthenorth/rails,mtsmfm/rails,Erol/rails,kmcphillips/rails,kmayer/rails,vipulnsward/rails,esparta/rails,kaspth/rails,Sen-Zhang/rails,tgxworld/rails,flanger001/rails,Sen-Zhang/rails,yhirano55/rails,rafaelfranca/omg-rails,bogdanvlviv/rails,palkan/rails,ngpestelos/rails,rossta/rails,yalab/rails,vipulnsward/rails,yawboakye/rails,sealocal/rails,koic/rails,gavingmiller/rails,arunagw/rails,kddeisz/rails,brchristian/rails,palkan/rails,BlakeWilliams/rails,aditya-kapoor/rails,Envek/rails,rbhitchcock/rails,yawboakye/rails,MSP-Greg/rails,yasslab/railsguides.jp,elfassy/rails,gavingmiller/rails,mathieujobin/reduced-rails-for-travis,esparta/rails,illacceptanything/illacceptanything,travisofthenorth/rails,maicher/rails,betesh/rails,starknx/rails,hanystudy/rails,odedniv/rails,rbhitchcock/rails,rails/rails,mtsmfm/rails,assain/rails,kirs/rails-1,yawboakye/rails,kaspth/rails,felipecvo/rails,mohitnatoo/rails,mijoharas/rails,kamipo/rails,assain/rails,Edouard-chin/rails,Erol/rails,printercu/rails,kenta-s/rails,deraru/rails,samphilipd/rails,utilum/rails,joonyou/rails,MSP-Greg/rails,illacceptanything/illacceptanything,ttanimichi/rails,stefanmb/rails,rafaelfranca/omg-rails,coreyward/rails,tjschuck/rails,Spin42/rails,pschambacher/rails,aditya-kapoor/rails,shioyama/rails,Stellenticket/rails,eileencodes/rails,illacceptanything/illacceptanything,pvalena/rails,tjschuck/rails,coreyward/rails,esparta/rails,eileencodes/rails,esparta/rails,jeremy/rails,Spin42/rails,prathamesh-sonpatki/rails,Envek/rails,yahonda/rails,bolek/rails,pvalena/rails,tjschuck/rails